Various standards for wireless communication are known, for example, to ensure interoperability between equipment from multiple vendors. The standards typically aim to ensure that an allocated spectrum for the wireless communication system is used efficiently.
One such widely adopted standard is the 3rd Generation Partnership Project (3GPP) standard. The 3GPP standard has had many revisions, including an evolution into the Long-Term Evolution (LTE) standards. The LTE standards also continue to evolve, such that there are multiple releases, one of which is the LTE standards Release 12 (e.g., Rel-12).
Network assisted interference cancellation and subtraction (“NAICS”) is a feature in LTE standard release 12. User equipment (“UE”) with NAICS can allow for substantial suppression of an interfering cell's contribution to a cellular communication signal received at the UE. One way to achieve NAICS is through joint demodulation of a transmission from the serving cell (which can be the desired transmission) with an interfering transmission from the interfering cell, for example, a neighboring interfering base station.
Joint demodulation can require jointly detecting the serving cell and interfering cell transmissions. Joint detection of the serving cell's transmission and the interfering cell's transmission can significantly increases a complexity of demodulation. Demodulation complexity can increase exponentially with the number of multiple input multiple output (“MIMO”) layers simultaneously detected. A transmission mode combination can be used to determine the number of layers that to be detected. Table 1 is an example a total number of layers to be detected for various combinations of serving cell and interfering cell transmission modes.
TABLE 1Serving cell TM/Interfering TM/Total # layerslayersLayersTM4/1LTM4/1L2TM4/1LTM4/2L3TM4/1LTM24TM2TM4/1L4TM2TM4/2L6TM2TM24
In comparison, without NAICS, a UE, employing two Rx antennas, can only require demodulating a maximum of two layers. As the optimal detection scheme that jointly demodulated all MIMO layers is not feasible due to a prohibitive complexity increase, sub-optimal schemes might be used. 3GPP has limited the complexity by specifying that the maximum number of layers in the demodulation is three (the rest are treated as noise). In addition, 3GPP has specified that in NAICS mode, the serving cell always uses quadrature phase shift keying (“QPSK”) and one layer.
3GPP has specified several receiver schemes for NAICS; however each receiver scheme performs well in some scenarios and poorly in others. Therefore, it is desirable to find a receiver scheme that performs well in a wide range of scenarios, while enabling the scheme to be implemented with the same hardware and keep the complexity approximately constant.